The present invention relates to foldable chairs, particularly wheelchairs and more particularly to an improved foldable wheelchair of lightweight non-metallic construction.
At present, the major structural components of most foldable wheelchairs are bent metal tubes. These foldable wheelchairs are generally heavy, unattractive in appearance and not sufficiently rugged for everyday use. In applications where the wheelchair must be formed of non-magnetic materials, such as used in Magnetic Resonant Imaging or MRI, non-magnetic stainless steel may be substituted for the steel tubing, substantially increasing the cost and weight of the wheelchair.
In view of these problems, there have been many attempts to design a foldable wheelchair using plastic as the major structural component. For example, U.S. Pat. No. 4,457,535 to Takeuchi, et al. discloses a wheelchair which may be formed primarily of plastic tubing and flexible material webs. Takeuchi employs a pair of yoke members pivotally connected at their lower ends to longitudinal tubular frame members and at their upper ends to a pair of tubular seat members. The intersection of the yoke members are connected for pivotal movement. The seat of the wheelchair is a web of flexible material hung between the tubular seat members. When the chair is folded and unfolded, the yoke members pivot about their pivotal connection in a scissor-like fashion. A disadvantage in this type of wheelchair is the time required to assemble the tubular members.
U.S. Pat. No. 4,770,432 to Wagner assigned to the Assignee of the present application attempts to avoid the disadvantages of tubular construction while still employing the advantages of plastic. The wheelchair employs molded side members and a pair of seat panels and back panels hingedly attached to the side panels. A pair of seat-supporting panels are located below the seat panels with their opposite ends hingedly attached to the side panels and their adjoining ends interconnected by a center hinge. The seat-supporting panels are arranged generally perpendicular to the hinge axis of the seat panels when the wheelchair is unfolded. The major components, including the wheels, seat, and side panels are formed of skinned polymeric foam, such as cast polyurethane foam. The wheelchair of this invention takes advantage of the advances in non-magnetic structural materials, particularly polymeric foam.
Although the Wagner wheelchair has advantages as a non-magnetic wheelchair, there are disadvantages. One of the major disadvantages is its weight. It was believed that the weight of the wheelchair could be maintained between 20 and 25 pounds; however, it was found that it was necessary to make the wheelchair much heavier to obtain adequate strength. Within the weight range of 20 to 25 pounds, the wheelchair was not considered to be strong enough to adequately support an adult. Therefore, further strengthening was required which increased the weight. The weakness of these wheelchairs was due in part to the use of the piano-type hinges which required seat support panels to provide additional support. In order to get adequate strength, the seat support panels had to be increased in size as well as the side panels and seat panels to support the weight of the adult. Further, the piano-type hinges require continued maintenance because they are exposed and susceptible to the accumulation of dirt, etc. Further, there were substantial costs in assembling the wheelchair because the piano-type hinges had to be attached in at least nine different locations. There is also the disadvantage of the piano-type hinges working loose and having to be reconnected and further maintained.
What is needed is a foldable wheelchair employing non-magnetic materials which can be easily assembled, easily maintained and lightweight. Such a wheelchair would have to be simple in construction, rugged, foldable or collapsible and take advantage of the advances in plastic and non-magnetic structural components. The wheelchair of this invention provides such a wheelchair.